A mystery South African man who acted as a sign-language interpreter at Nelson Mandela’s memorial service was a “fraud” who simply made “childish hand gestures” for hours as he stood on stage.

Deaf groups say the man, who has not yet been identified, made no sense in any language to those relying on him around the world, and did not seem to know the recognised signs for South Africa, Mr Mandela’s clan name Madiba, President Jacob Zuma or former President Thabo Mbeki.

As a result, they say, he had the effect of marginalising the deaf community, which was “contrary to everything Mandela fought for”.

The embarrassing revelation also raises questions about the security at the landmark event, which was attended by 91 heads of state and government including Barack Obama and David Cameron.

President Barack Obama stands next to the sign language interpreter after making his speech (AP)

The interpreter, who wore the clearance pass of a government official, stood just feet from Mr Obama as he made his widely-praised speech, and also interpreted for South Africa’s President Jacob Zuma, who apparently faces such a high threat level that he recently spent £12.4m on security upgrades to his private home.

The latest embarrassment was compounded by the news that Archbishop Emeritus Desmond Tutu’s house in Cape Town was burgled as he spoke at the event.

David Buxton, the CEO of the British Deaf Association, called on the South African authorities to “name and shame” the man who, he said, had acted in a way that was “disrespectful and hurtful” to deaf people around the world.

While some South Africans took to Twitter to claim the man had been signing in a South African language such as Xhosa or Zulu, Mr Buxton said he was purely making “childish hand gestures and clapping, it was as if he had never learn a word of sign language in his life”.

“It was hours of complete nonsense,” he said. “He is clearly a fraud who wanted to stand on stage with big and important people. It’s quite audacious if you think about it,” he said.

“It is incredibly disrespectful and hurtful to the deaf community.”

Bencie Woll, Professor of Sign Language and Deaf Studies at the University College London

Mr Buxton said the man had provided sign language for a speech for Mr Zuma at a military event last year. At that appearance, a deaf person in the audience videotaped the event and gave it to the federation for the deaf, which analysed the video, prepared a report about it and submitted a formal complaint to the African National Congress (ANC).

Sign language experts in South Africa said that all of the country’s 11 official languages were covered by the same signs, and they saw none of them used, nor any of the facial gestures that usually feature.

Ingrid Parkin, principal of the St Vincent School for the Deaf in Johannesburg, said she had received complaints from deaf people from around the world about the “gibberish” interpretation.

“This man himself knows he cannot sign and he had the guts to stand on an international stage and do that,” she said.

Footage from a South African news channel how their sign language interpreter's translation differed from that being provided by the on stage signer

Martie Miranda, a sign language instructor at the University of the Free State, said a simple phone call to DeafSA would have prevented the spectacle, which marginalised deaf viewers and was “contrary to everything Mandela fought for”.

It remains unclear whether the man was sourced by the government which organised the event, the ruling ANC or the national broadcaster the SABC.

The government said it was still looking into how the man was recruited. The SABC could not be reached for comment.

&lt;noframe&gt;Twitter: wilma newhoudt - Shame on this male so called interpreter on the stage. What is he signing? He knows that the deaf cannot vocally boo him off. Shame on him !&lt;/noframe&gt;

The ANC confirmed it had used him “as a volunteer” at several events previously, including its centenary celebrations in Bloemfontein last year.

“We’ve never had any complaints before,” spokesman Keith Khoza said.

But Wilma Newhoudt-Druchen, an ANC MP and the vice-chairperson of the Deaf Federation of SA (DeafSA), told the City Press newspaper that the DeafSA had submitted a report about the man to the party in 2012 but received no response.

&lt;noframe&gt;Twitter: Francois - &lt;a href="http://www.twitter.com/newhoudt" target="_blank"&gt;@newhoudt&lt;/a&gt; &lt;a href="http://www.twitter.com/BrunoDruchen" target="_blank"&gt;@BrunoDruchen&lt;/a&gt; &lt;a href="http://www.twitter.com/ANC_KKhoza" target="_blank"&gt;@ANC_KKhoza&lt;/a&gt; please get him off this is an embarrassment, no signs make sense, he is moving his arms try to look busy&lt;/noframe&gt;

&lt;noframe&gt;Twitter: PHOLOHO SELEBANO - &lt;a href="http://www.twitter.com/newhoudt" target="_blank"&gt;@newhoudt&lt;/a&gt; I know for a fact that DeafSA has made complaints, I have complained about it. But nothing is being done.&lt;/noframe&gt;